1. Field of the Invention
The present invention relates in general to a system and method for self-referencing a sensor that is used to detect if a biomolecular binding event occurred in a sample solution flowing along side a reference solution in a micron-sized deep flow channel. In one embodiment, the sensor and micron-sized deep flow channel are incorporated within a well of a microplate.
2. Description of Related Art
The performance of sensors based on optical detection techniques such as surface plasmon resonance (SPR), waveguide grating-based surface sensing, and surface or bulk scattering is generally affected by the designs and characteristics of the sensors, the optics, and by the environmental fluctuations. Unwanted sensitivity to environmental fluctuations including temperature change, mechanical vibration, and source drift (among others) is the most common problem affecting the performance of the sensors. Existing instruments like the Biacore® S51 which is made and sold by Biacore AB in Uppsala, Sweden are equipped with temperature control features which help minimize the effect of temperature fluctuations on the performance of the sensor. However, these types of instruments are expensive, and temperature control alone cannot correct for all environmental factors.
Other instruments attempt to diminish the impact of environmental fluctuations by providing a self-referencing method and/or a common environment for the reference and detection regions such that any environmental fluctuations can be referenced out. Three such instruments have been described in U.S. Pat. No. 6,200,814 B1 and EP1021703 B1 (Malmqvist et al.) and U.S. Pub. No. US2003/0022388 A1 (Roos et al.). Malmqvist et al. disclose methods and devices for controlling the fluid flow over a sensing surface within a flow cell such that selective sensitization of discrete sensing areas is permitted and selective contact of the discrete sensing areas with a sample fluid flow is provided. And, Roos et al. discloses a method for adjusting the position of the interface between fluids in the longitudinal direction of the flow cell by controlling the relative flow rates of the fluids.
One shortcoming of these instruments is that their surface sensors do not cover the whole width of the flow cell and as a result more than one surface sensor is required to cover the whole width of the flow cell in certain embodiments. Thus, in order to reference out any environmental fluctuations or non-specific biomolecular binding, at least two surface sensors are required in the flow cell, one for the referencing and one for the detection. By using more than one spatially separated sensor, the optics required for the detection are increased by the number of sensors added. As a result, there may be a physical limitation of how close the sensors can be positioned together and the number of sensors that can be used in the flow cell. Also, the different sensors may experience different environmental fluctuations and may have different characteristics and performances. All of these differences add to the uncertainty and hence can adversely affect the accuracy of detecting a biomolecular binding event.
Another shortcoming of these instruments is that they rely on a dynamic interface between the multiple laminar flows and then use the movement of the fluid interface as a key component of their referencing methodology. While both sample and reference fluids are present in the flow cell, the interface between the two fluids is adjusted to place the sample fluid stream exclusively over the sensor, then the fluid interface is further modified (via flow rate, etc.) so as to place the reference fluid over the same sensing region, thereby presenting a reference signal. While this method efficiently utilizes a single sensing region for both sample and reference fluids, the movement of the fluid interface can cause a disruption of the laminar flows, promote mixing of the streams, and thereby degrade the signals. Furthermore, accurate movement of the fluid interface requires impeccable control over the dimensions of the fluidic channel, fluid flow rates, etc. In addition, due to the movement of the fluid interface, the sample and reference signals are not measured at the same time which will decrease the accuracy of the self-referencing method.
Accordingly, there is a need for a system and method for self-referencing a sensor that addresses the aforementioned shortcomings and other shortcomings of the traditional instruments. This need and other needs are satisfied by the system and method of the present invention.